Wow, they really figured TV was a disposable medium back then, didn't they? I've heard of shows remaking scripts from other shows, and there's a Bionic Woman episode that's a remake of a Six Million Dollar Man episode -- but the same show doing the same script twice, five years apart? I've never seen that before.
There were more than one of the BIONIC WOMAN/SIX MILLION DOLLAR MAN remakes. I don't remember how many offhand, but the one I remember most involved Jaime and Rudy/Steve and Oscar getting stranded on a deserted island with an assassin after Rudy/Oscar. A lot of effort went into reusing effects while handwaving in new stories to justify them, as well.
As far as BEWITCHED is concerned, reusing scripts was prevalent in the '60s for series that went from B/W to color. It was mostly happenstance that the new, color versions all had a new Darren as well. Several Lost In Space B/W episodes were redone in color.